The polyphenylene ethers and processes for their preparation are well known in the art. They are described in Hay, U.S. Pat. No. 3,306,874 and U.S. Pat. No. 3,306,875 and Blanchard et al, U.S. Pat. No. 3,219,625 and U.S. Pat. No. 3,219,626, all of which are incorporated by reference. Other patents which show the preparation of polyphenylene ethers include Price et al, U.S. Pat. No. 3,382,212; Kobayshi et al, U.S. Pat. No. 3,455,880; Bennett and Cooper, U.S. Pat. No. 3,796,689; Bennett and Katchman, U.S. Pat. No. 3,787,362; Cooper U.S. Pat. No. 3,733,307; Cooper and Bennett, U.S. Pat. No. 3,733,299 and Cooper and Bennett, U.S. Pat. No. 3,900,445, all of which are incorporated by reference.
The processes most generally used to produce the polyphenylene ethers involve the self-condensation of a monovalent phenol in the presence of an oxygen-containing gas and a catalyst comprising a metal-amine complex.
These reactions are usually carried out in the presence of an organic solvent and the reaction is ordinarily terminated by removal of the catalyst from the reaction mixture. In the prior art, this has been done by the use of aqueous solutions of acetic acid, sulfuric acid or chelating agents such as glycine, nitrilotriacetic acid or its sodium salts. The use of the sodium salts of nitrilotriacetic acid results in the formation of a copper-nitrilotriacetic acid complex which is not very soluble in the organic reaction mixture or in the antisolvent. Portions of this complex are carried over into the precipitated polyphenylene oxide when the antisolvent is added.
It has now been found that nitrogenous salts of nitrilotriacetic acid form complexes with copper that are retained in the organic reaction mixture when an antisolvent is added to precipitate the polyphenylene oxide resin. This results in a polyphenylene oxide having a decreased level of copper as the resulting nitrilotriacetic acid-copper complex is made soluble in the organic effluent on antisolvent precipitation of the polyphenylene oxide resin.
As used herein, the term nitrogenous salt is used to describe the amine salts and the substituted guanidine salts of the above-mentioned nitrilotriacetic acid.